1. Field of the Invention
This invention relates to Bluetooth™ and 802.11 wireless communication systems, and more particularly to a method and apparatus for a dual-mode radio in a wireless communication system.
2. Description of Related Art
Wireless communication systems facilitate high-speed connectivity and data and voice transport from point-to-point and point-to-multipoint bases. Exemplary wireless communication systems include “Bluetooth™1 protocol” systems that facilitate the transport of data between Bluetooth™ devices such as wireless headsets, cellular phones, laptop computers and personal digital assistants (PDAs), and “IEEE 802 protocol” systems that facilitate the transport of data over wireless local area networks (WLANs), which include devices such as desktop and laptop computers. 1 Bluetooth™ is a trademark of Bluetooth SIG, Inc.
As is well known, Bluetooth™ is a global specification standard for radio communications operating at 2.4 GHz radio frequencies. Bluetooth™ devices (i.e., those that comply with the Bluetooth™ Specification) replace normal cable connections using short-range radio links. Bluetooth™ technology is featured in cordless telephony, intercom, FAX and LAN access, and dial-up networking applications. Bluetooth™ wireless communication protocols are implemented in wireless headsets, cellular phones, PDAs, printers, and other mobile devices. Bluetooth™ technology is described in more detail in a specification published by the Bluetooth™ Special Interest Group (SIG), entitled “Specification of the Bluetooth System, version 1.1”, electronically available to the public via the well-known Internet at <http://www.Bluetooth.com>, published on Feb. 22, 2001, referred to herein as the “Bluetooth™ Specification”, and incorporated for reference herein in its entirety for its teachings on Bluetooth™ flow control, signals, devices and communication protocols and schemes.
Bluetooth™ devices typically communicate with other Bluetooth™ devices using either a “piconet” communication network topology or a “scatternet” communication network topology. Details regarding the Bluetooth™ communication protocols, piconet and scatternet communication networks are described in detail in the Bluetooth™ Specification. Specifically, the piconet networks are described in Section 1 of Part B of the Bluetooth™ Specification. The scatternet networks are described in Section 10.9 of Part B of the Bluetooth™ Specification.
A piconet is defined in the Bluetooth™ Specification as a communication system including two or more Bluetooth™ devices that share a common frequency hopping pattern and a common “Access Word” (or “access code”). Access codes are pre-defined bit patterns that are transmitted to a Bluetooth™ device at the beginning of “data packets.” In addition to providing other functions, access codes are used for device synchronization and identification purposes. As defined in detail in section 4.1 of the Bluetooth™ Specification, data is communicated between Bluetooth™ devices in the form of data packets. The data packets have a pre-determined format defined by the Bluetooth™ Specification. As defined therein, a data packet includes an “access code”, a “packet header” and a “payload” of data bits. Details regarding packets and access codes are described in more detail in Section 4.1-2 of the Bluetooth™ Specification.
At a minimum, a piconet comprises two or more Bluetooth™ devices, such as, for example, a portable PC and a cellular phone that communicate with each other via the piconet. A piconet can comprise a maximum of eight connected devices. When establishing a piconet, one and only one Bluetooth™ device acts as a master device of the piconet. The master device initiates a connection to one or more slave devices. Any device in a piconet that is not a master device is, by definition, a slave device. Master-slave roles can be exchanged once a piconet is established. A master can become a slave, and a slave can become a master. Bluetooth™ master and slave devices utilize various Bluetooth™ protocols to exchange data.
Bluetooth™ wireless communication protocols aid in implementing various Bluetooth™ applications. Bluetooth™ applications utilize various links, or connections, to communicate between master and slave devices. As described in Part B, “Baseband Specification”, Sections 2.1 and 11, of the Bluetooth™ Specification, Bluetooth™ communication systems use a frequency hopping spread spectrum (FHSS) scheme (referred to hereinafter as the “FH scheme”) to communicate between master and slave devices. Frequency hopping modulation comprises the well-known method of repeatedly switching channels or frequencies during transmission of data. FH schemes require that the channel switching or “hopping” follow a specified algorithm so that devices can independently determine frequency-hopping (FH) sequences (i.e., they follow ordered lists of frequencies).
As described in the incorporated Part B, “Baseband Specification”, Section 2.1, of the Bluetooth™ Specification, Bluetooth™ communication protocols determine FH sequences using the Bluetooth™ device address and the clock of a master device. The FH sequences are determined to allow associated slave devices on a piconet to independently determine the FH sequences. Bluetooth™ communication protocols use a Bluetooth™ FH kernel to select the FH sequences and to map the FH sequences to hop frequencies.
As is well known, the various IEEE 802.11 communication protocols (referred to hereinafter as “802.11”) are global standards for radio communications operating at 2.4 GHz radio frequencies. One exemplary well-known IEEE 802.11 communications protocol is the IEEE 802.11b protocol (referred to hereinafter as “802.11b”). The 802.11b protocol allows 802.11b devices (i.e., those that comply with the 802.11b standard) to operate at high data transmission rates (e.g., 11 Mbps). The 802.11b protocol is particularly useful in implementing Wireless Local Area Networks (WLANs). 802.11b devices are described in more detail in a standard produced by the IEEE 802 Working Group, entitled “IEEE Std 802.11b-1999”, electronically available to the public via the well-known Internet at <http://standards.ieee.org>, referred to herein as the “802.11b Specification”, and incorporated for reference herein in its entirety for its teachings on 802.11b flow control, signals, devices and communication protocols and schemes. Another exemplary IEEE 802.11 communications protocol is the newly emerging IEEE 802.11g. Some embodiments of the invention are described below using the IEEE 802.11b protocol as an exemplary communications protocol. However, this is not meant as a limitation to the present invention as the present inventive method and apparatus contemplates use of any of the IEEE 802.11 communication protocols and future variants. Therefore, the generic “IEEE 802.11” term is used throughout the remainder of the specification to encompass all IEEE 802.11 communication protocols.
The 802.11 communications protocols (e.g., 802.11b) have options for FH schemes and direct sequence spread spectrum (DSSS) schemes (referred to hereinafter as “DS schemes”) to communicate between devices on the WLAN. Direct sequence modulation comprises a well known method of transmitting data across a single channel without hopping to other channels. DS schemes commonly use data redundancy during transmission for error correction purposes. The 802.11b equipment currently manufactured typically uses only the DS schemes. From the point of view of the utilization of the ISM band the 802.11b DSSS equipment is distinct from the Bluetooth™ protocol equipment because the 802.11b DSSS equipment occupies a fixed allocation of bandwidth. Although the 802.11b standard defines 11 DSSS channels in the ISM band, 802.11b DSSS equipment typically uses only channels 1, 6 and 11. The 802.11b DSSS carriers have a 3 dB bandwidth around 11 MHz with first zeros in their spectrum 22 MHz apart. Thus, in a simple view, the 802.11 systems (e.g., 802.11b systems) and the Bluetooth systems interfere with one another when the Bluetooth™ protocol frequency hops within the 22 MHz segment corresponding to the channel used by the 802.11.
It is desirable to operate both Bluetooth™ protocol devices and 802.11 protocol devices within close proximity to one another. For example, a laptop can include both a Bluetooth™ protocol device for wireless communication with a Bluetooth™ wireless mouse and an 802.11 protocol device for wireless communication with an 802.11 WLAN access point.
Disadvantageously, heretofore when Bluetooth™ and 802.11 protocol devices operate in close proximity, interference can be produced adversely affecting communication using both protocols. Interference can be created because both protocols operate on the 2.4 GHz ISM frequency band. Specifically, over-air interference and saturation of one transmitter by another transmitter can occur when a Bluetooth™ protocol antenna is in close proximity (e.g., within one-half meter) of an 802.11 protocol antenna. As is well known, interference increases the probability of reception errors. In any data communication system, it is desirable to reduce reception errors.
Therefore, a need exists for a method and apparatus for a dual-mode radio that reduces reception errors in devices contemporaneously using both Bluetooth™ protocol and 802.11 protocol devices in close proximity. The method and apparatus should adequately maintain adequate data transmission rates for both protocols. The present invention provides such a dual-mode radio method and apparatus.